Calcium channel blockers were identified as a method for the control of hypertension, as reported by Fleckenstein et al., Z. Kreislaufforsch, 56, 716 (1967), and are routinely used in the control of hypertension. Three calcium channel blockers are currently of clinical significance in the United States, verapamil, nifedipine and diltiazem. All three achieve their anti-hypertensive effect by inhibiting the entry of calcium ions into vascular smooth muscle. The ultimate effect is vasodilation.
Hypertensive hormones, such as the renin-angiotensin system (RAS), the vitamin D system, and the parathyroid hypertensive factor (PHF), are all causative factors in stimulating the increase of calcium ions in vascular smooth muscle. PHF is disclosed and described in copending patent application Ser. No. 327,450.
It has been found that calcium supplements, in dietary form, may inhibit the RAS, PHF and vitamin D systems, [Park et al., Am. J. Physiol., 235, F22 (1978); Park et al., Am. J. Physiol., 240, F70 (1981); Kotchen et al., Am. J. Cardiol., 62, 41G (1988); Bukoski et al., B.B.R.C., 147, 1330 (1987); Inoue et al., B.B.R.C., 152, 1388 (1988); Baran et al., J. Clin. Invest., 77, 1622 (1986); Lewanczuk et al., Am. J. Hypertens. (in press)] and are, therefore, beneficial in decreasing calcium uptake in vascular smooth muscle. An untoward effect of calcium supplementation is that the increased bio-availability of calcium partially negates the inhibitory effect on the endocrine system. Calcium channel blockers, by limiting the uptake of calcium in vascular smooth muscle, are beneficial, but have been found to stimulate some endocrine systems, such as the RAS system. [Kotchen et al., Am. J. Cardiol., 62 41G (1988); Matsumara et al., J. Pharmacol. Exp. Ther., 241, 1000 (1978); Resnick et al., Fed. Proc., 45, 2739 (1986)]. Utilization of calcium channel blockers may be limited by excessive vasodilation, negative inotropy, excessive depression of the sinus nodal rate, atrial-ventricular nodal conduction disturbances and interference with non-vascular smooth muscle contraction. A combination therapy which minimizes the amount of calcium channel blocker required to achieve the desired anti-hypertensive effect is desirable.